Discs are Items present in both games of the Phantasy Star Online series. In Phantasy Star Online, they were only used to learn new Techniques. In Phantasy Star Online, they teach both Techniques and Photon Arts to the player that uses them.
They were found anywhere from level 1 to 30 in PSO, while they are only present from level 1 to 15 in PSO2 (level 11+ Discs are only found on Very Hard mode).
Discs can be obtained from anything in the original PSO, and at any level. Higher level Discs appear on higher difficulties.
In PSO2, Discs from level 1 to 10 may be easily found for any of the 6 basic Photon Arts of each weapon and the 4 basic Technics of each element from anything on Normal or Hard mode. Level 11 to 15 Discs, as well as any level of Disc for the 3 rare Photon Arts and Technics to each weapon and element, can only be found on Very Hard mode.